If you’ve followed true crime at all over the past six years, you already know the date: April 24, 2018. That’s the day investigators arrested Joseph James DeAngelo — the Golden State Killer — at his home outside Sacramento, ending a four-decade hunt that had consumed careers, books, and entire online communities. What made the arrest possible wasn’t a confession or a lucky fingerprint. It was investigative genetic genealogy, and for cold cases in Los Angeles and everywhere else, nothing has been the same since.
The Los Angeles Times’ coverage of the arrest captured the disorientation of the moment: a case most detectives assumed would never close was suddenly closed, using websites built for hobbyist family-tree research. DeAngelo pleaded guilty in June 2020 to thirteen murders. And police departments across the country — very much including those working LA County’s deep backlog of unsolved homicides — started asking the obvious question: what else can this technique do?
How Investigative Genetic Genealogy Actually Works
Here’s the part most headlines skip, and honestly, it’s the best part — because the method is genuinely clever.
Traditional forensic DNA matching uses a small set of markers (the CODIS system) compared against databases of known offenders. If your suspect has never been arrested and swabbed, CODIS gives you nothing. Investigative genetic genealogy — IGG, if you want to sound like you work the cases — takes a completely different route:
- Build a SNP profile. Crime-scene DNA is processed to read hundreds of thousands of single-nucleotide polymorphisms, the same kind of dense genetic snapshot consumer ancestry tests produce.
- Upload to opt-in databases. That profile goes into GEDmatch or FamilyTreeDNA — the two databases that permit law-enforcement matching — to look not for the suspect, but for the suspect’s relatives. A second cousin who took a DNA test for fun can be the thread that unravels everything.
- Build the tree. Genealogists then do old-fashioned research — birth records, obituaries, census data, newspaper archives — constructing family trees from those distant matches and narrowing toward people who fit the case: right age, right place, right time.
- Confirm conventionally. IGG produces a lead, not an arrest. Investigators still need a direct DNA comparison — often from a discarded item — before anyone is charged.
The privacy questions here are real, and the field knows it. After a 2019 controversy, GEDmatch switched to requiring users to explicitly opt in to law-enforcement matching. The U.S. Department of Justice issued an interim policy on forensic genetic genealogy in 2019, restricting the technique to violent crimes and unidentified human remains, and requiring that investigators exhaust traditional methods first. Maryland went further in 2021, passing the first state law requiring judicial sign-off. This is a tool being built and regulated in real time.
What It Means for Los Angeles Cold Cases
Los Angeles County is, bluntly, the mother lode. Decades of unsolved homicides sit in LAPD and Sheriff’s Department files, many with preserved biological evidence collected long before anyone imagined it could be read this way. The Golden State Killer case itself had a Southern California chapter — DeAngelo’s crimes as the “Original Night Stalker” included murders in Ventura, Orange, and Santa Barbara counties — so local investigators didn’t need convincing that the technique works on California cases.
But there’s a second application that gets less attention and matters just as much: the dead who have no names.
The Los Angeles County Medical Examiner handles thousands of cases a year, and a sobering number of decedents are never identified by conventional means — no fingerprint match, no dental records, no missing-persons report that fits. These are the John and Jane Does, some of whom have waited in case files since the 1960s and 70s. Volunteer organizations like the DNA Doe Project (founded in 2017) and private labs like Othram (founded in 2018, specializing in degraded forensic samples) have been applying genetic genealogy to exactly these cases nationwide, returning names to people who died anonymous. Every identification is potentially two cases resolved at once: the coroner’s unidentified-remains file, and a family’s missing-person mystery somewhere else.
For an office whose public history runs through the most famous unsolved cases in American crime — this is the agency that autopsied the Black Dahlia, a case where the surviving evidence predates DNA science entirely — the idea that biology preserved in an evidence locker can still speak after fifty years is not abstract. It’s the job now.
The Limits, Because There Are Limits
A good true-crime reader is a skeptical one, so let’s be honest about what IGG can’t do.
It needs DNA — enough of it, in good enough condition, from the right person. Plenty of cold cases have no surviving biological evidence, or evidence so degraded that even specialized labs can’t build a usable profile. It needs database matches; communities underrepresented in consumer DNA testing produce thinner trees and slower results. It’s labor-intensive — tree-building on a tough case can take months of skilled work. And it’s expensive, which is why so many agencies lean on grants, nonprofits, and crowdfunded lab work.
It also doesn’t solve cases by itself. The genealogy gets you to a door; detectives still have to walk through it with evidence that stands up in court. The forensic record of the twentieth century is full of techniques that were oversold before they were understood — as we covered in our look at the O.J. Simpson case’s forensic legacy, the 1994–95 trial put DNA evidence itself on trial, and the lessons about contamination, chain of custody, and courtroom credibility still apply to every new method that follows.
But with all those caveats: hundreds of cases nationwide have been resolved with IGG since 2018. That’s not hype. That’s a scoreboard.
Why This Era Feels Different
Cold cases used to go cold for good. The file went to a warehouse, the detective retired, the family learned to live without answers. What investigative genetic genealogy has changed is the direction of time in these cases — evidence now gets more useful as science advances, not less. A swab collected in 1978 by a criminalist who couldn’t have imagined the internet may close a case in the 2020s.
For Los Angeles, with its unmatched archive of famous and forgotten unsolved deaths, that’s a genuinely new chapter. The next decade of LA cold-case news is going to be written, in part, by genealogists.
Frequently Asked Questions
What is investigative genetic genealogy?
It’s a technique that uploads a crime-scene DNA profile to opt-in consumer genealogy databases to find a suspect’s relatives, then uses traditional family-tree research to narrow down candidates. Investigators confirm any lead with a direct DNA comparison before making an arrest.
What was the first major case solved with genetic genealogy?
The Golden State Killer case. Joseph James DeAngelo was arrested in April 2018 after investigators matched crime-scene DNA to his distant relatives in a genealogy database. He pleaded guilty in 2020 to thirteen murders committed across California in the 1970s and 80s.
Can genetic genealogy identify unidentified remains?
Yes — it’s one of the technique’s most important uses. Organizations like the DNA Doe Project work with coroner and medical examiner offices to put names to unidentified decedents, some of whom have been in case files for decades.
Does law enforcement have access to my ancestry DNA test?
Not from the major testing companies directly. Law-enforcement matching is limited to databases where users have opted in, such as GEDmatch and FamilyTreeDNA, and federal policy restricts the technique to violent crimes and unidentified human remains.